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Glycogen Storage Diseases

Glycogen Storage Disease Overview

Glycogen storage diseases (GSDs) are a group of inherited genetic disorders that cause glycogen to be improperly stored in the body. People with glycogen storage diseases have a buildup of abnormal amounts or types of glycogen in their tissues.

Glycogen is the storage form of glucose in our bodies. Glucose is a simple sugar, which is a form of carbohydrate. It is found in many foods and is the main source of energy in our bodies.

The main types of glycogen storage diseases are categorized by number and name. They include:

Type I (Von Gierke disease) – this is the most common type of glycogen storage disease, and accounts for 90% of all glycogen storage disease cases

Since glycogen is primarily stored in the liver or muscle tissue, glycogen storage diseases usually affect functioning of the liver, the muscles, or both. The glycogen storage diseases that mainly affect the liver are types I, III, IV, and VI. The glycogen storage diseases that mainly affect muscles are types V and VII. Type II affects nearly all organs, including the heart.

Glycogen storage diseases are caused by a genetic enzyme defect that is inherited from both parents. Normally, enzymes help convert glucose into glycogen for storage. Other enzymes convert the glycogen back to glucose when quick energy is needed, as in exercise. In a person with a glycogen storage diseases, some of these enzymes are defective, deficient, or absent. This causes the buildup of abnormal amounts and types of glycogen in liver and/or muscle tissues.

Since glycogen storage diseases are hereditary, the primary risk factor for is having a family member with this disease.

Glycogen Storage Disease Symptoms

The symptoms of a glycogen storage disease depend on its type. The following is a list of common glycogen storage disease symptoms:

Low blood sugar

Enlarged liver

Slow growth

Muscle cramps

Symptoms of specific types of glycogen storage diseases include:

Type I - Von Gierke Disease

Enlarged liver and kidneys

Low blood sugar

High levels of lactate, fats, and uric acid in the blood

Impaired growth and delayed puberty

Bone thinning from osteoporosis

Increased mouth ulcers and infection

Type II - Pompe's Disease

Enlarged liver and heart

In severe cases, muscle weakness and heart problems develop

In severe cases, infants may suffer heart failure by the age of 18 months

Milder forms of type II may not cause heart problems

Type III - Cori's Disease

Swollen abdomen due to an enlarged liver

Growth delay during childhood

Low blood sugar

Elevated fat levels in blood

Possible muscle weakness

Type IV - Anderson's Disease

Growth delay in childhood

Enlarged liver

Progressive cirrhosis of the liver (which may lead to liver failure)

May affect muscles and heart in late-onset type

Type V - McArdle's Disease

Muscle cramps during exercise

Extreme fatigue after exercise

Burgundy-colored urine after exercise

Types VI, IX - Hers' Disease

Liver enlargement occurs, but diminishes with age

Low blood sugar

Type VII- Tarui's Disease

Muscle cramps with exercise

Anemia

Type VIII

Muscle weakness

Anemia

Increased levels of uric acid

Glycogen Storage Disease Diagnosis

Glycogen storage disease is usually diagnosed in infancy or childhood as a result of the above symptoms. If your child's doctor suspects a glycogen storage diseases, he or she will ask about your child's symptoms and medical history, then perform a physical exam. The doctor will perform tests to rule out or confirm the diagnosis. These tests may include:

MRI scan – a test that uses magnetic waves to make pictures of the inside of the body

Glycogen Storage Disease Treatment

Treatment will depend on the type of glycogen storage disease and the symptoms. The following general treatment guidelines apply to people who have glycogen storage diseases that affect the liver, or types I, III, IV, and VI. Your child's doctor will develop a treatment regimen based on your child's specific symptoms.

The goal of treatment is to maintain normal blood glucose levels. This may be done with:

A nasogastric infusion of glucose in infants and children under age two

Dietary changes, including:

In children over age two, frequent small carbohydrate feedings are given throughout the day. This may include uncooked cornstarch. (Uncooked cornstarch provides a steady slow-release form of glucose.)

Elimination of foods that are high in fructose or lactose (type I only)

Allopurinol (Aloprim, Zyloprim) may be prescribed to reduce uric acid levels in the blood. This is done to prevent gout and kidney stones.

This next group of treatment guidelines applies to people who have glycogen storage diseases that affect the muscles, or types V and VII. Your child's doctor will develop a treatment regimen based on your child's specific symptoms.

The goal of treatment is to avoid muscle fatigue and/or cramps induced by exercise. This is done by:

Regulating or limiting strenuous exercise to avoid fatigue symptoms

Improving exercise tolerance by oral intake of glucose or fructose (fructose must be avoided in people with type I), or an injection of glucagon

Eating a high protein diet

There is no way to prevent glycogen storage diseases. However, early treatment can help control the disease once a person has it. If you have a glycogen storage disease or a family history of the disorder, you can talk to a genetic counselor when deciding to have children.